Effect of Homoharringtonine on Differentiation and Apoptosis of Human Leukemic Cell.

Homoharringtonine (HHT) is a cephalotaxine ester derived from an evergreen tree found wildely throughout southern China, which has antileukemic activities against a variety of acute myeloid leukemic cells especially acute promyelocytic leukemia and acute monocytic leukemia. In order to illustrate the mechanisms of HHT in the treat of leukemia, we assessed the effect of HHT on several human leukemic cell lines, including promyelocytic leukemic cell HL60 and erythroblastic leukemic cell line K562. The differentiation of K562 cells and HL60 cell was determined by nitro tetrozolium blue reduction test (NBT) and differentiation antigens assay. The apoptosis of leukemic cells induced by HHT was analyzed by morphological observation, DNA gel electrophoresis, flow cytometry assay and terminal deoxyribonucleotidyl transferase-mediated dUTP-biotin nick and labeling method. Our results showed that the capacity of K562 and hL60 cells to reduce NBT was gradually increased after exposure to HHT at a lower concentration. The capacity of K562 cells to reduce NBT was higher after exposure to 0.01ug/ml of HHT than 0.005ug/ml of HHT. It indicated that the capacity of cells to reduce NBT was dependent on HHT concentration and time of exposure.

The fraction of HL60 cells displaying CD14 or CD11b increased significantly whereas that of displaying CD33 decreased after incubated with 0.001ug/ml of HHT for ten days. This data indicated that HHT induced hl60 cells to mature into monocyte-like cells.

Characteristic changes for apoptosis emerged in K562, and HL60 cells after exposured to HHT at a concentration 0.05–100ug/ml and 0.00505ug/ml respectively. The percentage of apoptotic cells in K562 and HL60 cells increased according to the concentration or exposure time of HHT. There was no DNA ladder in DNA gel electropheresis when K562 and HL60 cells incubated with HHT at a concentration lower than 0.05ug/ml and 0.005ug/ml respectively, even if the incubation time was long enough.

In this study, we confirmed that HHT has differentiative and apoptotic effects on human leukemic cells. The extent of HHT induced differentiation and apoptosis was dependent on drug concentration and time exposure.